1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor. In addition, the present invention relates to an electrophotographic image forming method, apparatus and process cartridge using the electrophotographic photoreceptor.
2. Discussion of the Background
Recently the growth of electrophotographic image forming apparatus using a photoreceptor such as copiers, printers and facsimiles is remarkable. In particular, photo-printers capable of recording digital information using light have been drastically improving in recording qualities and reliability. This digital recording technique is applied to copiers as well as photo-printers. The digital copiers to which this digital technique is applied have various image forming functions. Therefore it is considered that the demand for the digital copiers increases more and more.
As the photoreceptor used for such image forming apparatus, photoreceptors using an organic photosensitive material are typically used because of having advantages such as low manufacturing costs, low toxicity and good film formability over inorganic photosensitive materials such as selenium.
Photoreceptors using an organic photosensitive material include single-layered photoreceptors, and multi-layered photoreceptors. Single-layered photoreceptors include a photosensitive layer which is formed on an electroconductive substrate and which typically includes a charge generation material, a charge transport material and a binder resin. The photosensitive layer is typically formed by coating a coating liquid including such constituents on a substrate using a coating method such as dip coating methods.
In multi-layered photoreceptors, the photosensitive layer typically includes a charge generation layer which is formed on an electroconductive substrate and which includes a charge generation material, and a charge transport layer which is formed on the charge generation layer and which includes a charge transport material. The multi-layered photoreceptors typically include an undercoat layer which is formed between the substrate and the charge generation layer, and/or a protective layer which is formed on the charge transport layer, to improve the image qualities and durability of the resultant photoreceptors.
At the present time, laser diodes (LDs) and light emitting diodes (LEDs) are used as light sources for the photo-printers because of being small in size, and having a relatively low cost and good reliability. The LEDs which are typically used for the photo-printers emit light having a wavelength of 660 nm. The LDs which are typically used for the photo-printers emit near infrared light. Therefore, a need exists for a photoreceptor having high sensitivities over a wavelength range including the visible region and the near infrared region.
The wavelength range over which an electrophotographic photoreceptor has sensitivity almost equal to the wavelength range over which the charge generation material used in the photoreceptor has photosensitivity. Therefore, various kinds of materials, such as azo type pigments, polycyclic quinone type pigments, trigonal system selenium, phthalocyanine pigments and the like, have been developed for the charge generation materials.
Among these materials, titanyl phthalocyanine pigments (hereinafter sometimes referred to as TiOPc), which have been disclosed in Japanese Laid-Open Patent Publications Nos. 3-35064, 3-35245,3-37669, 3-269064 and7-319179, are very useful for a photoreceptor for image forming apparatus such as printers and copiers, which use an LED or LD as a light source. This is because titanyl phthalocyanine is sensitive to light having a relatively long wavelength of from 600 to 800 nm.
A photoreceptor used for electrophotography such as Carlson process and the like processes is required to have the following charge properties as well as the high sensitivity to the specific light mentioned above:
(1) good charging ability such that a high electric potential can be formed and maintained in a dark place;
(2) good charge decaying ability such that the electric potential previously formed on the photoreceptor rapidly decays and the residual potential is low when the photoreceptor is exposed to light; and
(3) good charge stability such that the photoreceptor can maintain a good charging ability and a good charge decaying ability even when the photoreceptor is used for a long time.
In particular, in high sensitive photoreceptors such as photoreceptors including TiOPc, the charging ability thereof tends to deteriorate and the residual potential tends to increase when the photoreceptors are repeatedly used. Namely, the photoreceptors including TiOPc have an insufficient charge stability. Therefore, a need exists for a photoreceptor which includes a TiOPc and which has good charge stability.
In addition, another problem which occurs is that undesired black spot images are observed in background area of images when a reverse developing method is used. In particular, after a photoreceptor is preserved under high temperature and high humidity conditions, this black spot problem frequently occurs. Therefore, a need also exists for a photoreceptor which does not cause such a black spot problem.
Because of these reasons, a need exists for a photoreceptor maintaining high sensitivity and good charge properties, and producing good images without causing undesired images such as black spots even when repeatedly used for a long period of time and even after the photoreceptor is preserved under high temperature and high humidity conditions.
Accordingly, an object of the present invention is to provide a photoreceptor which maintains high photosensitivity and good charge properties, and capable of producing good images without causing undesired images even when repeatedly used for a long period of time and even after the photoreceptor is preserved under high temperature and high humidity conditions.
Another object of the present invention is to provide an image forming method using a photoreceptor, by which good images can be stably produced at a high speed without hardly causing undesired images such as black spots even when images are repeatedly produced for a long period of time and even after the photoreceptor is preserved under high temperature and high humidity conditions.
Yet another object of the present invention is to provide an image forming process cartridge and apparatus in which good images can be stably produced at a high speed without hardly causing undesired images such as black spots even when images are repeatedly produced for a long period of time and even after the apparatus and process cartridge are preserved under high temperature and high humidity conditions.
To achieve these objects, the present invention contemplates the provision of a photoreceptor including an electroconductive substrate, and a photosensitive layer formed on the substrate and including an organic pigment as a charge generation material, wherein the photosensitive layer includes at least an ion selected from the group consisting of a potassium ion (K+), a sodium ion (Na+), a nitrate ion (NO3xe2x88x92), a formate ion (HCOOxe2x88x92) , a nitrite ion (NO2xe2x88x92), a chloride ion (Clxe2x88x92), a bromide ion (Brxe2x88x92), and an ammonium ion (NH4+). The concentrations of the ions are preferably not greater than 50 ppm, not greater 200 ppm, not greater than 50 ppm, not greater than 100 ppm, not greater than 50 ppm, not greater than 100 ppm, not greater than 50 ppm, and from 10 to 300 ppm, respectively, relative to total amount of the organic pigment.
Preferably, the organic pigment is a titanyl phthalocyanine pigment. The concentrations of a potassium ion (K+) a sodium ion (Na+), a nitrate ion (NO3xe2x88x92), a formate ion (HCOOxe2x88x92), a nitrite ion (NO2xe2x88x92), a chlorine ion (Clxe2x88x92), a bromine ion (Brxe2x88x92), and an ammonium ion (NH4+) in the titanyl phthalocyanine pigment are preferably not greater than 50 ppm, not greater 200 ppm, not greater than 50 ppm, not greater than 100 ppm, not greater than 50 ppm, not greater than 100 ppm, not greater than 50 ppm, and from 10 to 300 ppm, respectively.
Alternatively, the photosensitive layer includes one or more water-soluble inorganic salts in an amount not greater than 1000 ppm relative to the organic pigment. Preferably the organic pigment is a titanyl phthalocyanine pigment.
The titanyl phthalocyanine pigment preferably has an X-ray diffraction spectrum in which main peaks are observed at Bragg 2xcex8 angle of 9.6xc2x0xc2x10.2xc2x0, 24.0xc2x0xc2x10.2xc2x0 and 27.2xc2x0xc2x10.2xc2x0; 7.5xc2x0xc2x10.2xc2x0, 25.3xc2x0xc2x10.2xc2x0 and 28.6xc2x0xc2x10.2xc2x0; 9.3xc2x0xc2x10.2xc2x0, 13.1xc2x0xc2x10.2xc2x0and 26.2xc2x0xc2x10.2xc2x0; or 9.0xc2x0xc2x10.2xc2x0, 14.2xc2x0xc2x10.2xc2x0, 23.9xc2x0xc2x10.2xc2x0 and 27.1xc2x0xc2x10.2, when a specific X-ray of Cu-Kxcex1 having a wavelength of 1.541 xc3x85 irradiates the titanyl phthalocyanine pigment.
The photosensitive layer preferably includes a charge generation layer including the charge generation material, and a charge transport layer including a polycarbonate resin having a triaryl amine structure in its main chain and/or side chain.
In another aspect of the present invention, an electrophotographic image forming method is provided which uses the photoreceptor of the present invention mentioned above and which includes the steps of charging, light irradiating, developing and image transferring.
In yet another aspect of the present invention, an electrophotographic image forming apparatus is provided which includes an image bearing member, a light irradiating device, a developing device, and an image transferring device, wherein the image bearing member is the photoreceptor of the present invention mentioned above. A process cartridge including at least the photoreceptor of the present invention may be used for the image forming apparatus.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.